1. Field of the Invention
The present invention relates to a zinc oxide powder comprising plate-like zinc oxide particles.
2. Description of the Related Art
Zinc oxide (ZnO) is a material to which various functions such as electroconductive properties, thermoelectric properties, and piezoelectric properties can be imparted through a suitable material design. It is known that orienting a certain crystal plane is effective for enhancing these properties. For example, as a method for obtaining an oriented sintered body, a method is known in which plate-like particles are used as a raw material, a green body is prepared using a molding method such as tape casting or extrusion molding in which shearing force is applied to the plate-like particles, and this green body is sintered (for example, Patent Document 1 (JP10-139552A)).
To date, methods for preparing plate-like zinc oxide particles having various particle sizes have been proposed, and such particles mostly are dense, plate-like particles (see, for example, Non-Patent Document 1 (J. Vac. Sci. Technol. B28(2), C2C16-C2C19 (2010)), Patent Document 2 (JP4807569B), Patent Document 3 (JP3512838B), and Patent Document 4 (JP3559293B)). However, although a green body having a high degree of orientation can be easily prepared in the case where dense, plate-like zinc oxide particles having a particle diameter exceeding 1 μm are used as a raw material and a molding method as described above in which shearing force is applied is employed, it is difficult to uniformly disperse an additive substance such as a dopant. On the other hand, in the case where plate-like dense zinc oxide particles are fine, with the particle diameter thereof being no greater than several hundreds of nm, although it is easy to uniformly disperse an additive substance, sufficient application of shearing force to the particles is not achieved, and it is difficult to prepare a green body having a high degree of orientation. Thus, it is difficult to simultaneously achieve a high degree of orientation and uniform dispersion of an additive substance in a green body.
As another method for obtaining an oriented sintered body, a method in which a magnetic field is applied to a slurry is known (see, for example, Patent Document 5 (JP4378535B)). Although a green body having a high degree of orientation can be obtained by this method even when a fine raw material is used, a superconducting magnet needs to be used, and there is a problem of increased costs.